Method of making unsaturated compounds



Patented Nov. 3, 1942 UNITED STATES PATENT OFFICE Joy G. Lichty, Stow, Ohio, assignmto Wingl'oot Corporation, W of Delaware 11, Del., a corporation No Drawing. Application October 2, 1940,

Serial No. 359,409

9Clalms.

, unsaturated bodies by adding to the nitrile molecule an acyl radical and then removing the corresponding carboxylic acid by pyrolysis. If, in addition to the acyl radical, the saturated nitrile also contains a halogen radical, a hydrogen halide will also be split out toleave a cyano dioleflne, such as a cyano 1,3-butadienecompound, the particular compound obtained depending upon the halogenated nitrile selected as the starting material. Also, the starting material may be the intermediate corresponding to the compound resulting when the carboxylic acid has been removed, a halogen-alkyl-substituted acrylonitrile, in which case only hydrogen halide is split oil by the pyrolysis.

' The pyrolysis is believed to proceed in such manner that there is produced alkyl-substituted acrylonitriles containing one or more halogen atoms in the molecule by the splitting out of a carboxylic acid and the cyano diolefines are then formed by the removal of this halogen in the form of a halogen acid. The reaction may be illustrated by the following equations, indicating the probable course of the pyrolysis of alpha acyloxy alpha (l-chloroethyl) -propionitrile:

CHFC-CN OCOR HG CHaC-CN (E RCOUH CHCI OH:

C=(I1CN Cl CH:

CHz=C-CN (IJHCI HO] CHFCH C=CH1 CH1 N The symbol R" in the foregoing formulae indlcates an alkyl group, usually, but may denote other radicals.

It will be noted that, while two different chloro acrylonitriles may be obtained, each of these can give rise to a 2-cyano 1,3-butadiene by splitting out hydrogen chloride. Usually, a mixture of all tained, together with unchanged starting material, and the 2-cyano 1,3-butadiene is separated therefrom by appropriate means, as by fractional distillation. It will also be observed that the na- 5 ture of the acyl radical is not critical since this is removed during the course of the reaction in the form of the corresponding carboxylic acid.

The method may be applied to the preparation of various substituted 2cyano 1,3-butadiene compounds, such as z-cyano isoprene, 2-cyano 3-ethyl 1,3-butadiene, 2-cyano 3-chloro 1,3-butadiene,

2-cyano 3-bromo 1,3-butadiene, 2-cyano 4-methyl 1,3-butadiene, 2cyano 4-ethyl' butadiene, and homologous compounds in which other alkyl groups are substituted in the cyano butadiene molecule. The appropriate propionitrile is selected for pyrolysis. Thus, if it is desired to prepare 2-cyano 1,3-butadiene. itself or a substituted 2-cyano 1,3-butadiene, then it is necessary to select an alpha acyloxy propionitrile which is alpha substituted by a halogen alkyl group in which the carbon chain containing the halogen has two carbon atoms, in order that a four carbon chain will result. Only a haloethyl substituent produces 2-cyano 1,3-butadiene. Likewise, a halo isopropyl substituent results in a 3-methyl substituted 2-cyano butadiene but a halo alkyl group in which the chain containing the halogen is longer than two carbon atoms gives a 4-alkyl substituted cyano butadiene. 0f couis'e, a longer carbon chain may be present as a substituent on the alkyl group.

Obviously, the halogen atom may be chlorine, bromine or other halogen since it is removed during the pyrolysis and does not characterize the final product. Likewise, as mentioned, the nature'of the acyl radical in the starting material is not critical since it is similarly removed from the molecule. In fact, any acyl radical which 40 can be readily added to the propionitrile molecule to constitute the starting material, can be used, among such radicals being formyl, acetyl, propionyl, butyryl, benzoyl, toluyl, xyloyl, oxalyl and phthalyl.

The pyrolysis is carried on under conditions which will result in the removal of a molecule of carboxylic acid and a molecule of hydrohalide acid from a molecule of the propionitrile, the conditions for this purpose being selected according to the nature of the starting material. Generally speaking, a temperature ranging from 350-700 C. will be employed, with a preferred range for best results in the neighborhood of 400-550' C. The pressure is usually kept low,

three products, and perhaps others, will be ob* althoughjhls may range upward to atmospheric vent any tendency of the unsaturated product to polymerize during the course of the reaction. For this purpose there may be used hydroquinone, phenol and diphenyl para phenylene diamine, as well as other compounds having this function.

To illustrate the procedure followed in preparing the compounds of the invention, the following example is given to which, however, the invention is not limited.

Example The pyrolytic apparatus used in this experiment was a A" standard pipe, a 2 length heated by an electric heating unit to a temperature of 500525 C. The iron tube was filled with quartz pellets and through it was passed a total of 590 grams of the acetylated cyanohydrin of t l-chloro- Z-butanone,

The cyano compound was passed through the system at the rate of 4.5 grams per minute at a pressure of 50-65 mm. The total recovery was 555 grams. Since some of the pyrolytic products are polymerizable, it is desirable to dissolve a polymerization inhibitor, such as hydroquinone, in the product before pyrolysis. The 555 grams of material were washed thoroughly with salt water to remove the acetic acid split off and then dried and distilled in the presence of hydroquinone as inhibitor. The following fractions were obtained:

Fraction B. P. C. Grams 1 -95 o./21 mm 160 2 95-150 cm mm 265 Fraction #l-was redistilled to yield a number of fractions, of which the low boiling fraction, boil- 1 ing at 44-50" C./73 mm. polymerized in a short period of time on standing at room temperature. The solid formed by the polymerization was removed and ashed with ether. Its analysis ave the following results: percent N found: 17.67; calo. for

CHz=CH-C=CH:

17.75. Thus, the product in this fraction is evidently cyano 1,3-butadiene. lieved to proceed as follows:

OCOCHa dus- 012101-0-015,

The method is applicable, as stated, to the preparation of cyano diolefines generally, and espe- The reaction is becially to the preparation of substituted 2-cyano 1-,3-butadienes, 2-cyano isoprene being obtainable by substituting in the foregoing example the acetylated cyano hydrin of 3-chloro-3-methyl-2- butanone and 2-cyano-4-methyl 1,3-butadiene being likewise obtainable by the pyrolysis of the acetylated cyanhydrin of 3-chloro-2-pentanone. The formyl or benzoyl cyano hydrins will give the same results, as will compounds with other acyl radicals substituted forthe acetyl radical.

- While there have been described above the preferred embodiments of the. invention, it will be apparent to those skilled in the art that various modifications and changes may be made therein ,without departing from the spirit of the invention or from the scope of the appended claims.

I claim:

1. A method of preparing cyano dioleflnes which comprises pyrolyzing an acyloxy propionitrile containing a halogen alkyl radical having at least two carbon atoms to split of! a carboxylic acid and hydrogen halide.

,2. A method of preparing cyano 1,3-butadienes which comprises pyrolyzing an acyloxy propionitrile containing a halogen alkyl radical having a chain of two carbon atoms to split of! a carboxylic acid andhydrogen halide.

3. -A method-of preparing cyano 1,3-butadienes which comprises pyrolyzing an alpha acyloxy propionitrile containing a halogen alkyl radical having a chain of two carbon atoms to split ofi a carboxylic acid and hydrogen halide and treating the reaction product to separate a cyano 1,3- butadiene.

4. A method of preparing 2-cyano'1,3-butadienes which comprises pyrolyzing an alpha acytoxy proprionitrile containing a halogen alkyl radical having a chain of two carbon atoms to split off acetic acid and hydrogen halide and recovering a 2-cyano 1,3-butadiene from the reaction product.

5. A method of preparing cyano diolefines which comprises pyrolyzing in the presence of a polymerization inhibitor an acyloxy proprlonitrile containing a halogen alkyl radical having at least two carbon atoms to split off a carboxylic acid and hydrogen halide.

6. A method of preparing Z-cyano 1,3-butadiene which comprises pyrolyzing an alpha acyloxy, halo alpha ethyl propionitrile to split on a carboxylic acid and a hydrogen halide and recoverin 2-cyano 1,3-butadiene from the reaction product.

"I. A method of preparing a 2-cyano 1,3-butadiene in which the 4-position is unsubstituted and the 3-position carries a substituent from the group consisting of hydrogen and alkyl which comprises pyrolyzing an alpha acyloxy hola alpha alkyl propionitrile in which the longest chain in the halo alkyl group contains two carbon atoms and recovering from the reaction product a 2- cyano 1,3-butadiene compound.

8. A method of preparing z-cyano 1,3-butadiene which comprises pyrolyzing an alpha acetoxy chloro ethyl propionitrile to split 01f acetic and hydrochloric acids and recovering 2-cyano 1,3- butadiene from the reaction product.

9. A method of preparing 2-cyano 1,3-butadiene which comprises pyrolyzing alpha-acetoxyalpha (l-chloroethyl) propionitrile to split on acetic and hydrochloric acids and treating the reaction product to recover the 2-cyano 1,3-butadiene.

' JOY G. LICHTY. 

